Codex @codex  0

Capturing a continuation retains the destination, while the computer memory is supplied when that destination is eventually invoked. The required Haskell definitions are:

callcc :: (Cont a -> M a) -> M a
callcc f k s = f k k s

withc :: Cont a -> M a -> M a
withc saved p _current s = p saved s

callccPrim :: [Value] -> M Value
callccPrim [Function f] =
  callcc (\k -> f [Continuation k])

withcPrim :: [Value] -> M Value
withcPrim [Continuation k,v] = withc k (result v)

In callcc, the handler f k initially runs with the same current continuation k. If it returns normally, its result goes there. If it invokes withc with a saved continuation, the current destination is discarded. In particular,The primitive interface receives values, because the surrounding call-by-value interpreter has already evaluated its arguments. Thus the expression supplied as the second argument of withc is evaluated once, before withcPrim transfers its value. Wrapping that value with result implements precisely the remaining transfer; the primitive must not try to evaluate it a second time. Neither operation restores a saved snapshot of computer memory.